In the processing of cobalt it is often desirable to convert cobalt metal and oxides to pure water soluble cobalt salts. This is done typically by dissolution of the cobalt source material in mineral acids. The resultant soluble salts are converted to extrafine cobalt metal powder by a variety of techniques that include oxalates, carbonates, hydroxides, etc.
A disadvantage of dissolution by mineral acids is the formation of undesirable gaseous by-products such as hydrogen, chlorine, and NO.sub.x gases.
There are essentially no purification steps by these processes. Therefore the starting source itself must be relatively pure.
Therefore, a method which allows impure cobalt material to be converted to a pure cobalt salt and hence to a pure metal powder without undesirable by products would be desirable.
The following U.S. Patents relate to cobalt processing: U.S. Pat. No. 4,184,868 relates to a method for producing extra fine cobalt metal power by digesting cobalt pentammine chloride in ammonium hydroxide to obtain a black precipitate which contains cobalt and which is thereafter reduced to the metal powder. U.S. Pat. Nos. 4,214,894, 4,233,063, and 4,278,463 relate to improvements in 4,184,868 in which the ammonia solutions are processed to recover any cobalt therein. U.S. Pat. Nos. 4,395,278 and 4,469,505 relate to improvements in 4,184,868 in which fine cobalt metal powder is produced having reduced tailings.
U.S. Pat. No. 4,214,895 relates to a process for producing cobalt metal powder which involves treating an aqueous solution of a soluble cobaltic ammine halide with a sufficient amount of a soluble metallic hydroxide to form a cobalt containing precipitate which is thereafter reduced to metallic cobalt.
U.S. Pat. No. 4,218,240 relates to a method for producing cobalt metal powder by forming a solution of a cobalt hexammine compound from an acid solution and treating the solution with a metallic hydroxide to form a precipitate which is reduced to cobalt metal powder. U.S. Pat. Nos. 4,348,224 and 4,381,937 relate to improvements in the process described in 4,218,240 which involve removal of copper and silver from the cobalt. U.S. Pat. No. 4,452,633 relates to an improvement in the process described in U.S. Pat. Nos. 4,218,240 and 4,348,224 in which the silver is recovered.
U.S. Pat. No. 4,329,169 relates to a process for producing fine particle size cobalt metal powder absent tailings by heating an aqueous solution of soluble cobalt ammine halide to decompose the halide and form a cobalt containing precipitate which is reduced to the cobalt metal powder.
U.S. Pat. No. 4,409,019 relates to a process for producing fine cobalt metal powder from pieces of relatively pure cobalt by dissolving the cobalt pieces in an aqueous solution of hydrogen iodide and iodine and forming a cobalt containing solid which is subsequently reduced to a fine cobalt metal powder.